Non-symmetrical differential transformer



Jan. 16, 1962 J. cHAss 3,017,590

NON-SYMMETRICAL DIFFERENTIAL TRANSFORMER Filed May 29. 1958 Output Voltage 32 F INVENTOR JACOB CHASS BY P024522" Armaiure Core Dlsplocemem fl w d ATTORNEY 3,017,590 NON-SYMMETRICAL DIFFERENTIAL TRANSFORMER Jacob Chass, Philadelphia, Pa, assignor to International Resistance Company, Philadelphia, Pa.

Filed May 29, 1958, Ser. No. 738,770 5 Claims. (Cl. 336-136) This invention relates to the construction of a differential transformer and more particularly to a differential transformer having a long range of travel for the armature core and its null position at one end thereof.

Heretofore, differential transformers were composed of a tubular bobbin of non-conductive, non-magnetic material having three individual coils of conductive wire wound thereon in side-by-side relation and an armature core of magnetic material movably disposed within the bobbin as shown in United States Letters Patent No. 2,507,344. The center coil being the primary coil and the two end coils, each of which is composed of the same number of turns, being the secondary coils with the secondary coils being connected in bucking series arrangement. By bucking series arrangement it is meant that the coils are connected so that when an AC. current input is placed on the primary coil the output of one of the secondary coils is ofan opposite phase to the output of the other secondary coil. When the armature core is in a position where it extends across the entire primary coil and projects beyond each end of the primary coil and across the same number of turns of each of the secondary coils it is at its null position, i.e., the output of each of the secondary coils are equal and of opposite phase so that the total output of the transformer is zero. If the armature core is moved in either direction from its null position it will extend across more turns of one of the secondary coils and less turns of the other secondary coil so that the output of the transformer increases. The maximum output of the transformer is obtained when the armature core has moved to a position where it still extends across the entire primary coil but projects only across one of the secondary coils. However, in such differential transformers, the maximum length of travel of the armature core from its null position to the position providing the maximum output of the transformer is small, being a maximum of A the length of the transformer. In my copending application, Serial No. 734,882, filed May 13, 1958, entitled Differential Transformer there is disclosed a construction of a differential transformer having a permissible travel of the armature core of approximately /2 the length of the transformer. The previously known type of differential transformer described above and the differential transformer described in my co-pending application, Serial No. 734,882 are both symmetrical type transformers, i.e., movement of the armature core in either direction from the null position produces outputs of equal magnitude. However, there are requirements for a difierential transformer which has evena longer permissible displacement of the armature core and which does not have to be symmetrical.

It is therefore an object of this invention to provide a construction of a differential transformer having a longer travel of the armature core. It is a further object of this invention to provide a construction of a differential transformer in which the permissible displacement of the armature core is substantially the length of the transformer. It is another object of this invention to provide a nonsymmetrical dilferential transformer. It is still another object of this invention to provide a non-symmetrical differential transformer which has a long travel of the armature core. Other objects of the invention will in part be obvious and will in part appear hereinafter.

United States Patent The invention accordingly comprises the features of construction, combination of elements, and arrangement of parts, which will be exemplified in the construction hereinafter set forth, and the scope of the invention will be indicated in the claims.

For a fuller understanding of the nature and objects of the invention, reference should be had to the following detailed description taken in connection with the accompanying drawing, in which:

FIGURE 1 is a longitudinal sectional view of the differential transformer of this invention;

FIGURE 2 is a circuit diagram of the differential transformer of this invention; and

FIGURE 3 is a graph showing the output of the differential transformer with respect to the displacement of the armature core.

Referring to FIGURE 2 of the drawing, the difierential transformer of this invention in general comprises an elongated primary coil 10 having a uniform number of turns per unit length, a first secondary coil 12 extending along a portion of the primary coil 10 at one end thereof, a second secondary coil 14 extending along the remaining portion of the primary coil 10, a core 16 of magnetic material fixedly mounted within the primary coil 10 andextending across the first secondary coil 12 and an armature core 18 of magnetic material movably disposed within the coils. The second secondary coil 14 has a progressively increasing number of turns per unit length from its end adjacent the first secondary coil 12 to the other end thereof and is connected to the first secondary coil 12 in bucking series arrangement. First secondary coil 12 is composed of a sufficient number of turns to provide a null position of armature core 18 as close as possible to fixed core 16, as will be explained.

In operation, when an input current is placed across primary coil 10, it will induce through fixed core 16 a constant output in first secondary coil 12 as indicated by line 30 in FIGURE 3. At the same time, primary coil 10 induces through armature core 18 an output in second secondary coil 14. When armature core 18 is positioned near fixed core 16 so that it crosses a number of turns of second secondary coil 14 equal to the number of turns of first secondary coil 12, the magnitude of the output of each of the secondary coil 12 and 14 will be equal. Since the secondary coil 12 and 14 are connected in bucking series arrangement, the outputs will be of opposite phase. Thus, the two equal outputs will cancel each other so that the total output of the transformer will be zero and the armature core 18 will be at its null position. If armature core 18 is moved from its null position to the right as viewed in FIGURE 2, it will extend across a greater number of turns of second secondary winding 14 so that the output induced in second secondary coil 14 will increase as indicated by line 32 in FIGURE 3. Since the output induced in first secondary coil 12 remains constant, as the output of secondary coil 14 increases the total output of the transformer also increases, as indicated by line 34 in FIGURE 3, until a maximum output is obtained when armature core 18 is at the end of the second secondary coil 14. Thus, the armature core 18 has a permissible displacement from its null position at substantially one end of the transformer to the other end of the transformer. Although in FIGURE 3, the output of the transformer is shown to increase linearly, it may follow any desired function which is determined by the function of the increase in turns per unit length of second secondary coil 14.

FIGURE 1 shows a preferred form of the differential transformer which comprises a tubular bobbin 36 of nonmagnetic, non-conductive material, such as a plastic or ceramic, having radially extending end flanges 38 and 40 and a plurality of radially extending additionally flanges,

42a to 42g, equally spaced therealong between end flanges 38 and 40. The flanges form a plurality of compartments, 44a to 4411, therebetween. First coils, 46a to 4611, of insulated electricallyconductive wire are wound around bobbin 36 in each of compartments 44a to 44g respectively. First coils, 46a to 46h are. each composed of the same number of turns and are connected together in series relation to provide primary coil 10. In end compartment 44a, a second coil 48 of insulated electrically conductive wire is wound over first coil 46a to provide first secondary coil 12. In each of the remaining compartments 44b to 44h a second coil, 50a to 50g respectively, of insulated electrically conductive wire is wound over each of first coils 46b to 46h respectively and the second coils 50a to 50g are connected together in series relation to provide second secondary coil 14. Coils 50a to 50g are composed of progressively increasing number of turns from coil 50a to ooil 50g as that coil 50a has the fewest number of turns and coil 50g has the largest number of turns. Second secondary coil 14, made up of coils 50a to 50g connected in series, in connected to first secondary coil 12, made up of coil 48, in bucking series arrangement. A tubular core 16 of magnetic material is fixedly mounted in bobbin 36, such as by a force fit, and extends across end compartment 44a which contains coil 48 providing first secondary coil '12. Armature core 18 of a rod of magnetic material is movably disposed within bobbin 36. If desired, a sleeve 52 of magnetic material can be placed around bobbin 36 and discs 54 and 56 of magnetic material placed against end flanges 38 and 40 to shield the coils and to reduce the reluctance of the magnetic flux path. Disc 56 is shown to be a flange on the end of core 16 but it can also be a separate member. Although bobbin 36 is shown having a plurality of flanges forming compartments in'which the various coils are wound, the transformer can be made with a bobbin which does not have the flanges and with the various coils wound thereon .in their proper position. However, a flanged bobbin is preferred since it facilitates the winding of the coils in their proper position.

It will thus be seen that the objects set forth above, among those made apparent from the preceding description, are efficiently attained and, since certain changes I may be made in the above construction without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawing shall be interpreted as illustrative and not in a limiting sense.

It is also to be understood that the following claims are intended to cover all of the generic and specific features of the invention herein described, and all statements of the scope of the invention which, as a matter of language, might be said to fall therebetween.

Having described my invention, what I claim as new and desire to secure by Letters Patent is:

1. A differential transformer comprising the combination of an elongated helically wound coil of electrically conductive wire having a uniform number of turns per unit length, a second coil of electrically conductive wire wound over a portion of said first coil, a third coil of electrically conductive wire helically wound over the remaining portion of said first coil, said third coil having an increasing number of turns per unit length thereof from one of its ends to its other end, said third coil being connected 0t said second coil in bucking series arrangement, a core of magnetic material Within said first coil and extending across said second coil, and an armature core of magnetic material movably disposed within said first coil.

2. A differential transformer comprising a tubular bobbin of non-magnetic, non-conductive material, a coil of electrically conductive wire helically wound around and along said bobbin and having a uniform number of turns per unit length, a second coil of electrically conductive wire wound over a portion of said first coil at one end of said first coil, a third coil of electrically conductive wire helically wound over the remaining portion of said first 'coil, said third coil having an increasing number of turns per unit legnth from said second coil to the other end of flanges between said end flanges, said flanges being equally spaced along said end flanges, said flanges being equally spaced along said bobbin and forming compartments therebetween, a first coil of electrically conductive wire wound on said bobbin in each of said compartments, each of said first coils being composed of the same number of turns and being connected in series arrangement to provide a primary coil, a second coil of electrically conductive wire wound over said first coil in one of the end compartments to provide a first secondary coil, a second coil of electrically conductive wire wound over said first coil in each of said other compartments, said second coils in said other compartments being connected together in series arrangement to provide a second secondary coil, the coils of said second secondary coil having increasing number of turns from the coil adjacent said first secondary coil to the coil at the other end of the bobbin, said second secondary coil being connected to said first secondary coil in bucking series arrangement, a core of magnetic material fixedly mounted within said bobbin and extending across the end compartment containing said first secondary coil, and an armature core of magnetic material movably disposed within said bobbin.

4. The differential transformer as set forth in claim 3 including a sleeve of magnetic material surrounding said bobbin and said coils and a disc of magnetic material References Cited in the file of this patent UNITED STATES PATENTS 2,424,766 Miner July 29, 1947 2,494,579 Pimlott Jan. 17, 1950 2,507,344 MacGeorge May 9, 1950 

